A gas turbine engine generally includes, in serial flow order, a compressor section, a combustion section, a turbine section and an exhaust section. In operation, air enters an inlet of the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section. Fuel is mixed with the compressed air and burned within the combustion section to provide combustion gases. The combustion gases are routed from the combustion section through a hot gas path defined within the turbine section and then exhausted from the turbine section via the exhaust section.
In particular configurations, the turbine section includes, in serial flow order, a high pressure (HP) turbine and a low pressure (LP) turbine. The HP turbine and the LP turbine each include various rotatable turbine components such as turbine rotor blades, rotor disks and retainers, and various stationary turbine components such as stator vanes or nozzles, turbine shrouds, and engine frames. The rotatable and stationary turbine components at least partially define the hot gas path through the turbine section. As the combustion gases flow through the hot gas path, thermal energy is transferred from the combustion gases to the rotatable and stationary turbine components.
Turbine engines also include one or more fuel nozzles for supplying fuel to the combustion section of the engine. Known fuel nozzles typically include one or more concentric tubes coaxially mounted so as to define one or more annular passages or conduits that allow for fluid to flow therethrough. More specifically, a typical fuel nozzle includes an external tube or heat shield having an inlet fitting at one end for receiving fuel and an atomizer nozzle at the other end for issuing atomized fuel into the combustor of a gas turbine engine. Thus, fuel can be introduced at the front end of a burner in a highly atomized spray from the fuel nozzle. Compressed air flows around the fuel nozzle and mixes with the fuel to form a fuel-air mixture, which is ignited by the burner. Thus, for typical fuel nozzles, the external heat shield is immersed in high temperature combustor gas while the inner fuel tube carries fuel at a much lower temperature than the compressed air. Elevated fuel temperatures can promote the formation of fuel-derived deposits that can unacceptably increase the total fuel nozzle flow restriction or change the flow velocity and/or jet shape. Further, due to the temperature differential, the external heat shield typically experiences thermal expansion differently than the inner fuel tube. More specifically, the external heat shield typically experiences thermal growth to a greater extent than the inner fuel tube.
In some fuel nozzles, the inner fuel tube(s) are rigidly connected to the external heat shield, e.g. using a welded or brazed joint. In such fuel nozzles, high stress concentrations can develop at the joint(s) due to thermal growth, thereby causing damage to the nozzle. Still further fuel nozzles may include detached inner fuel tube(s) and a detached external heat shield. In such embodiments, however, if the tube(s) and heat shield are completely decoupled and the external heat shield extends substantially the length of the nozzle and into the combustor, a variable size pocket can form at the combustor interface resulting in an auto-ignition risk.
Accordingly, the present disclosure is directed to a fuel nozzle that addresses the aforementioned issues associated with differing thermal expansion of nozzle components and the formation of fuel-derived deposits. More particularly, the present disclosure provides a fuel nozzle that compensates for thermal growth of the external heat shield relative to the inner fuel tube(s) during engine operation.